1. Field of the Invention
The present invention relates to the field of compression ignition (diesel) engine engineering, and more particularly to the field of controls and control systems for optimizing engine performance in a multi-fuel compression ignition engine suitable for use in automotive, marine, locomotive; mining, construction, agricultural, electricity generation and all other applications for compression ignition engines.
2. Description of Background Art
Every compression ignition engine comes equipped with a combustion strategy, a set of control parameters to the engine directing if, when, how, for how long, and how frequently to inject fuel and air into the cylinder combustion chamber. The combustion strategy of a contemporary compression ignition engine is embodied in an electronic control module (ECM) or power control module (PCM), which contains a set of fuel maps setting the engine control parameters for as many as fifteen to twenty different sets of operating conditions, such as engine start-up, idle, heavy load, high altitude, cold ambient temperature, and post start-up default.
Engine fuels, such as petroleum diesel; biofuels including biodiesel and triglycerides (consisting of vegetable oil and animal fat); and/or synthetic fuels derived from processes like Fischer-Tropsch can vary in such physical or chemical characteristics as their viscosity, density (specific gravity), thermal energy (calories or BTU's per pound, kilogram, gallon or liter), bulk modulus of compressibility, lubricity, and the relative complexity of the hydrocarbon molecules at which they release their energy during combustion. Given the same combustion strategy, or set of combustion commands, the physical or chemical properties of different fuels can in turn affect the timing and characteristics of combustion in a compression ignition engine. As an example, given a constant combustion strategy, different fuel types can affect operating parameters, such as the timing of fuel injections; the duration of injections; the quantity of fuel injected into the cylinder combustion chamber by each injection prior to, during, and after the piston reaches top-dead-center in the cylinder combustion chamber; the power output of the engine; and the composition and quantity of emissions from the combustion process.
Some compression ignition engines are equipped with a fuel system that alternates between two or more different diesel fuel types while the engine is operating. Accordingly, in a fuel system that alternates between two or more different fuel types having different physical or chemical properties, a need arises to vary the combustion strategy by affecting one or more engine control parameters according to which one of the fuels, or which combination of the two fuels, is presently supplying the fuel to the compression ignition engine.